1. Field of the Invention
The present invention relates generally to the field of helical piering systems. More specifically, the present invention discloses a modular helical piering system using shafts with a generally rectangular cross-section.
2. Statement of the Problem
Piering systems have long been used to lift and stabilize foundations of structures, and also in new construction. Some systems employ piles that are driven into the ground adjacent to the foundation, while other piering systems employ helical piles that are screwed into the ground. These piles are also used to anchor structures (e.g., large antennas, or pylons for high voltage lines) that are subject to large wind loads.
Conventional helical piles have an elongated shaft with a helical bearing plate permanently attached to the shaft adjacent to its lower end. The shaft can either be solid or tubular. For example, A. B. Chance Company of Centralia, Mo., markets helical piles having a solid shaft with a substantially square cross-section. The lower end of the shaft is beveled to form a point. The helical bearing plate is welded to the lower end of the shaft adjacent to the bevel. The length of the shaft is fixed, as are the diameter and location of the helical plate. In addition, some installations require several helical plates of different diameters spaced along the shaft. All of this can result in an substantial inventory problem to ensure that the appropriate helical piles are in stock for each job, particularly due to the size and expense of these helical piles.
It is also difficult to accurately predict the length of the piles that will be required for a specific job. Helical pilings are typically screwed into the ground to a point at which a predetermined torque limit is reached. It is difficult to predict what the depth of insertion will be when this torque limit is reached due primarily to the unpredictable nature of local soil conditions. Therefore, it is often necessary to add an extension to the shaft of the helical pile. For example, A. B. Chance Company markets an extension shaft having a square socket that fits over the upper end of the helical pile shaft. A bolt can be passed through aligned holes in the socket of the extension shaft and the upper end of the helical pile shaft to secure the extension shaft to the helical pile. A problem arises if the shaft of the helical pile is too long. In this case, the upper end of the shaft must be cut off and a new hole must be drilled through the shaft to secure the shaft to the support bracket needed to engage the foundation. This can be difficult and time-consuming in the field, particularly when dealing with a solid shaft.
Thus, a need exists for a helical piling system that is modular in design so that helical blades of various sizes and diameters can be used interchangeably, and various helical blades can be interchangeably combined with a shaft of a desired length. In addition, there is a need to be able to quickly and easily connect shafts to one another in the field to create a shaft assembly of a desired length.
Solution to the Problem. Nothing in the prior art teaches or suggests a modular helical piling system with tubular shafts having a rectangular cross-section that can be secured to one another in series by means of removable pins inserted through holes in the shafts. In addition, one or more helical blades can be readily secured to the shafts at desired locations by means of such pins. This modular approach allows the length of the shaft assembly and placement of the helical blades to be readily customized in the field to meet the specific needs of each job.